Multi-beam array antenna

ABSTRACT

A multi-beam array antenna assembly is disclosed, such assembly being adapted to form a plurality of simultaneously existing beams of radio frequency energy, each one of such beams having the gain of the entire antenna aperture and a different scan angle. The preferred embodiment of the contemplated assembly is fabricated, using printed circuit techniques and matching sections on a dielectric substrate, to form an array of antenna elements and constrained electrical paths for radio frequency energy between each one of the antenna elements and a number of feed ports. The electrical length of each one of such paths is adjusted so as to focus radio frequency energy in each one of the desired beams at a different feed port. The preferred embodiment also illustrates a multi-beam array antenna assembly having antenna elements spaced to increase the scan angle of each desired beam.

Tinned States Patent 1 1 1 ,761,936

Archer et a1. Sept. 25, 1973 1 MULTl-BEAM ARRAY ANTENNA PrimaryExaminerEli Lieberman [75] Inventors: Donald Archer; Robert J.Attorney-Philip J. McFarland, Joseph D. Pannone and Prickett, both ofSanta Barbara, Richard Sharkansky Calif; Curtis P. Hartwig, Lexington,

Mass. [57] ABSTRACT [73] Assignee: Raytheon Company, Lexington, Amulti-beam array antenna assembly is disclosed, such Mass. assemblybeing adapted to form a plurality of simultaneously existing beams ofradio frequency energy, each Flled' 7 May 1 1971 one of such beamshaving the gain of the entire antenna [21] Appl. No.: 142,149 apertureand a different scan angle. The preferred embodiment of the contemplatedassembly is fabricated, using printed circuit techniques and matchingsections [52] US. Cl. 343/754, 343/854, 333/84 M l b f f Im. CL q 14/06on a 1e ectrlc su strate, to orm an array 0 antenna [58] Field li 755771 elements and constralned electrical paths for radio fre quencyenergy between each one of the antenna elements and a number of feedports. The electrical length of each one of such paths is adjusted so asto focus [56] References Cited radio frequency energy in each one of thedesired UNITED STATES PATENTS beams at a different feed port. Thepreferred embodi- 3,52 ,l 2 8/1970 sakiotis et al. .t 343/854 ment alsoillustrates a multibeam array antenna assem- 3v623112 11/1971 PP etal343/727 bly having antenna elements spaced to increase the 3,392,3947/1968 Caballero v l 43/754 1 f h d d b 3,569,973 3/1971 Brumbaugh343/771 Scan ang e O eac eslre earn 3 Claims, 2 Drawing Figures 76 o 570-45b o 0 5d 0 57b 490 o Q o 579 i o M t A i 496, 476/ o o -.4 5c o 570496 Q -45c/ o q 47e 0 577 57 v r49 0 '45? o i f O Q o t 57% 4 219 9 47 o57g l 459 t 579 v r 57h o i 1 V 1 1 5 /7 a t 45/ 14 h o Q 57/ 49k 0 o 5Jo 57/ 0 471 Q 45/ Patented Sept. 25, 1973 2 Sheets-Sheet :3

v v Hk v o R Ev kkv 9% Ev o fiw INVENTORS DONALD H ARCHER ROBERT J.PR/CKEW' CURT/S P HARTW/G MULTI-BEAM ARRAY ANTENNA BACKGROUND OF THEINVENTION This invention pertains generally to array atennnas for radiofrequency energy and particularly to antennas adapted to form aplurality of simultaneously existing beams of such energy, the positionin space of each one of such beams being independent, within broadlimits, of the frequency of such energy.

It is known in the art that an array antenna may be arranged so that itproduces a plurality of simultaneously existing beams of radio frequencyenergy. If such an array is properly designed, each one of the beams hasthe gain and bandwidth of the entire antenna aperture. According to theart, a desired number of simultaneous beams may be obtained byconnecting each antenna element through a constrained electrical path toa plurality of feed ports, the constrained electrical path being made upof an electromagnetic lens which equalizes the time delay of theelectromagnetic energy between any given one of a number of feed portsand all points on corresponding planar wave fronts of either transmittedor received energy.

Any one of a variety of known electromagnetic lenses may be used. Forexample, the individual antenna elements in an array may be connectedthrough coaxial cables of varying lengths to radio frequency probes, thelatter being inserted in a parallel-plane lens to which the feed portsare also coupled at points along the focal arc of the lens. While suchan arrangement is satisfactory for many purposes, it has been foundthat, if air is the dielectric material in the parallel-plate lens, arelatively large lens is required. Consequently, a known multi-beamarray may find little, if any, application where space is at a premium,as in airborne applications.

It is known in the art that the size of a parallel-plate lens may bedecreased by using a dielectric material which has a dielectric constantgreater than that of air. The use of such material has, however, in thepast, been limited to applications in which a single beam is to beformed or the frequency of operation is to be limited within arelatively narrow band of frequencies because mismatches within theparallel-plate lens, or multiple reflections therein, combine toincrease sidelobe levels and to distort the shape of the desired mainbeams. With conventional multi-beam array antenna systems, it has beencustomary to use orthogonal probes to couple radio frequency energy toand from a parallel plate lens. In order that such energy may betransferred efficiently, it has been found that such probes should bespaced away from conducting side walls of the lens at a distance ofapproximately one-quarter wavelength of the microwave energy (at thefrequency of interest). Obviously, then, the bandwidth of the antennasystem is limited by such a requirement because the optimum quarter-wavespacing of the orthogonal probes will vary with changes in frequency.

Another problem which is experienced with conventional multibeam arrayantenna systems is that discrete radio frequency components, such astransmission lines and directional couplers, must be used along with anyknown parallel-plate lens. It is evident, therefore, that extreme caremust be taken in construction, assembly and use to ensure properconnection of the various elements making up such a multi-beam arrayantenna system. The magnitude of the problem may be appreciated when itis considered that literally thousands of radio frequency connectors arerequired in multi-beam array antennas of conventional design.

It is also characteristic of known multi-beam array antenna systems thatthe beam scan factor (meaning the ratio of the off-axis tilt of anyradiated wave front and the angular location of each feed port from areference line) is equal to 1. While such a characteristic is acceptablewhen a small number of beams is required or the off-axis tilt of any onebeam is not great, say not over 30", it has been found that such a beamscan factor limits the usefulness of many arrays. That is, when a wideangle system is desired, it becomes almost impossible with knowntechniques to maintain beam shape at large scan angles.

SUMMARY OF THE INVENTION AND DESCRIPTION OF THE DRAWINGS Therefore, itis a primary object of this invention to provide an improved arrayantenna system for producing a number of simultaneously existing beams,such system incorporating a parallel-plate lens using a dielectricmaterial having a dielectric constant greater than that of air.

It is another object of this invention to provide an improved arrayantenna system for producing a number of simultaneously existing beams,such antenna system being smaller in size than known antenna systems ofsuch type.

Still another object of this invention is to provide, for use in anarray antenna system of the type hereinbefore designated, a lens using adielectric material having a dielectric constant greater than thedielectric constant of air, such lens utilizing printed circuittechniques to avoid internal mismatch and spurious reflections and topermit coupling of the resulting lens in a most efficient manner to theremaining portions of the antenna systern.

A further object of this invention is to provide an improved multi-beamarray antenna system in which the number of required radio frequencyconnectors is reduced to a minimum.

A still further object of this invention is to provide an improvedmulti-beam array antenna system which is adapted to operate over a wideband of frequencies.

Another object of this invention is to provide an improved multi-beamarray antenna system which may be used in applications requiring largebeam scan angles.

These and other objects of this invention are attained generally byusing printed circuit techniques to form a multi-beam array antennaassembly on a common substrate having a dielectric constant greater thanthat of air, such assembly including the required antenna elements,transmission lines and microwave lens to focus radio frequency energy atpredetermined points along a focal arc of such lens, the transmissionlines and microwave lens being printed in such a way on the commonsubstrate as to form constrained paths for radio frequency energy, theassembly being completed by providing conventional coaxial connectorsfor coupling the microwave lens to external circuitry. For a morecomplete understanding of this invention, reference is now made to thefollowing description of a preferred embodiment of this invention asillustrated in the accompanying drawing, in which:

FIG. 1 is a block diagram, greatly simplified, of a multi-beam arrayantenna assembly according to our inventive concepts incorporated in adirection finder, the illustrated antenna assembly being partiallybroken away to better show the details of its construction; and

FIG. 2 is a plan view of the substrate, the antenna elements andportions of the transmission lines and microwave lens of the multi-beamarray antenna assembly shown in FIG. 1, such view illustrating howprinted circuit techniques may be applied in the construction ofmulti-beam array antennas.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, it maybe seen that the main sub-assemblies making up a direction finderincorporating the principles of this invention are a multi-beam arrayantenna assembly 10, a plurality (here 9) of receivers 11a through lli,a selector 13 and a utilization device 15. Except for the multi-beamarray antenna 10, the just enumerated main sub-assemblies of theillustrated system are preferably conventional in construction. Thus,each one of the receivers 11a through lli may be a known heterodynereceiver adapted to convert radio frequency sisgnals to intermediatefrequency signals derived from a different one of a similar plurality offeed ports (not numbered) of the multi-beam array antenna assembly 10.It is highly desirable that each one of the receivers 11a through lli bebroadband, meaning responsive to any radio frequency signal within, say,a bandwidth in the order of an octave of frequencies. The selector 15,here illustrated in an extremely simple form for expository purposes,consists of an input selector switch 171' and an output selector switch170, each having eight positions. Each one of such switches is operativesequentially to connect receivers 11b through lli to a detector 19.Receiver 11a is connected to a detector 21. The output terminals of thedetectors 19, 21 are connected to a threshold circuit 23, as adifferential amplifier, which in turn is connected, through a driver 25,to the output selector switch 170. To complete the circuit, each pole ofthe output selector switch 170 is connected, as shown, to a separate oneof a plurality of indicator lamps 27b through 27i in the utilizationdevice 15. It will be obvious, then, that the just-described selector l3and utilization device 15 is effective, using the output signals fromdetector 21 as a reference signal, so as to cause different ones of theindicator lamps 27b through 27i to be lighted when signals above apredetermined level are present at the output terminal of correspondingones of the receivers 11!) through 11h. It is equally obvious that theinput selector switch 171' and the output selector switch 170 may beoperated rapidly and cyclically so as to cause each one of theperiodically actuated ones of the indicator lamps 27b through 27i toappear to be continuously lighted, thereby to provide a visualindication of the particular receivers 11b through lli which produceoutput signals. The particular ones of the receivers 11b through lliwhich produce output signals, in turn, indicate which ones of the beamsformed by the multi-beam array antenna assembly 10 contain radiofrequency energy, i.e. the direction of the origin of received radiofrequency energy.

Obviously, the just-described apparatus is operative by reason of theinherent ability of an array antenna, as the multi-beam array antenna10, to form simultaneously existing beams. Thus, in FIG. 1, themulti-beam array antenna assembly 10 is seen to consist, from the bottomup, of a laminar arrangement made up from a first metallic ground plate31, a dielectric substrate 33 (on which circuitry 35 described in detailhereinafter is printed), a dielectric 37 and a second metallic groundplate 39 overlying the greater portion of the circuitry 35. It will berecognized that such an arrangement constitutes a conventional striplineconfiguration for providing constrained paths for radio frequency energybetween input terminals (the antenna elements) and output terminals (thecoaxial connectors to be mentioned). The laminar arrangement is fastenedtogether in any convenient manner, say by a number of bolts, as thosenumbered 41. In passing, it will be noted that the number of bolts 41 isfar in excess of the number required simply to hold the laminararrangement together. The excess number of bolts 41, which number mayvary as desired, serve to shield printed lines 47A through 47K andprinted lines 578 through 57I of the circuitry 35 from one another.

It is essential to the invention that the material from which thedielectric substrate 33 be fabricated have a dielectric constant, orindex of refraction, greater than that of air, here taken to be 1. Forefficiency of operation and ease of fabrication, it is desirable thatthe dielectric substrate 33 have a relatively low loss tangent and thatit be easily machined. For these reasons, it is here preferred that thedielectric substrate 33 be fabricated from a sheet of sintered magnesiumtitanate having a dielectric constant of approximately 16, althoughother materials may be used. For example, rutile (dielectric constantapproximately or an epoxy base loaded with rutile (dielectric constantapproximately 25) may also be used as the material for the dielectricsubstrate 33. It is preferred, although not essential, that thedielectric sheet 37 be fabricated from the same material as thedielectric substrate 33. At lower frequencies, say below S-band, theunbalance caused by using two different dielectric materials becomesinsignificant. As a matter of fact the dielectric sheet 37 and thesecond metallic ground plate 39 may be omitted from the laminar assemblyat such frequencies thereby converting the laminar arrangement to aconventional microstrip configuration. To complete the multi-beam arrayantenna assembly 10, a plurality (here 9) of conventional coaxialconnectors 43a through 43h are disposed to provide nine output terminalsfor such assembly.

Referring now to FIG. 2, it may be seen that the circuitry 35 within themulti-beam array antenna assembly 10 here consists of particular printedcircuits laid down on one surface of the dielectric substrate 33. Thus,an antenna element 45a is printed on the dielectric substrate 33 andconnected, through a printed line 47a, to coaxial connector 43a (FIG.1). It will be recognized that the directivity of antenna element 45a isthat of a monopole (or an end fed conductor) antenna, i.e. approximatelyso that radio frequency signals from any source located within a 180sector in the plane of the laminar arrangement are received by antennaelement 45 and directed, via coaxial connector 43a, to receiver 11a(FIG. 1).

Antenna elements 45b through 45k, each of which is similar to antennaelement 450, are connected through different lengths ofprinted lines 47bthrough 47k (each one of such lines including a matching section 49bthrough 49k) to a conductive surface of a parallel-plate lens 51. Theintersections of such matching sections and the parallelplate lens 51here describe an arc of a circle indicated by the dotted line marked 53.The second surface (sometimes referred to hereinafter as the focal areor the arc of best focus) of the parallel-plate lens 51 is indicated bythe dotted line 55. Matching sections 57b through 57i are printed alongthe focal arc of the parallelplate lens 51, as shown. Each one of suchsections, being faired into a different one of printed lines 57b through571', constitutes a feed port (not num bered) for a different beam. Eachone of such lines is, as shown in FIG. I, connected to a separate one ofthe coaxial connectors 43b through 43i. In passing, it will be notedthat the number of antenna elements 45b 'thr'ough 45k may; and'usually'will, differ from the number of feed ports. The number of theformer and their disposition determine the shape and, to some extent,direction of the beams while the number and disposition of the latterdetermine the number of the beams and, along with the antenna elements45b through 45k, the direction of the beams.

It will be recognized that, disregarding any mutual coupling between thevarious parts of the stripline configuration just described and anymismatches therein, the just-mentioned portions of circuitry 35, thedielectric substrates 33, 37 and the first and second metallic groundplates 31,39 constitute a two-dimensional constrained electromagneticlens system having 5 of freedom. That is, there are five independentvariables which may be changed in the design of the illustrated lenssystem: (I) the arrangement of the antenna elements 45b through 45k; (2)the length of each one of the printed lines 47b through 47k; (3) theshape of the parallel plate lens surface numbered 51 and the points ofintersection of each one of the matching sections 49b through 49ktherewith; (4) the shape of the parallel-plate lens surface numbered 53and the points of intersection of each one of the matching sections 57bthrough 591' therewith; and (5) the dielectric constant of the materialmaking up the dielectric substrate 33. It is known in the art, e.g. asshown in the paper entitled Wide Angle Microwave Lens for Line SourceApplications by W. Rotman and R. F. Turner (Transactions of Antennas andPropagation, pp. 623-632, published in November, 1963, by the Instituteof Electrical and Electronic Engineers, Inc., November, New York, N.Y.), that the first four parameters may be independently varied toproduce a scanning array antenna. Thus, according to Rotman and Turner,the first four parameters may be selected to provide an array antennaassembly similar to that here shown, i.e. one in which the antennaelements lie on a straight line and the locus of the points of bestfocus lie on the arc of a circle having its center on the axis ofsymmetry of a parallel-plate lens. According to Rotman and Turner, whenradio frequency energy is fed into the parallelplate lens from a feedport on the arc of best focus: (a) the electrical length of each path ofsuch energy between any such feed port through the parallel-plate lensand the transmission lines to any antenna element and thence to acorresponding point on a planar wave front (which results from thediffraction pattern of the antenna elements) equals, to any desireddegree (within, say, one-eighth ofa wavelength at the design frequencyof the radio frequency energy) the electrical length of the path of suchenergy from such feed port through the centrally located antenna elementto the same planar wave front; and (2) the scan angle (meaning theangular deviation from broadside) of the resulting beam ofelectromagnetic energy is the negative of the scan angle of the feedport (meaning the angular deviation of the feed port to which radiofrequency energy is fed to the parallel-plate lens from the axis ofsymmetry of such lens). The shape of the beam is, as is well known, afunction of illumination taper, and size of the antenna aperture, ie thenumber and spacing of antenna elements, and the frequency of the radiofrequency energy. A moments thought will make it clear that the designcriteria of the scanning array antenna just described may serve as thebasis for the design ofa multibeam array antenna for transmitting radiofrequency energy. Thus, if instead of using a single feed port along thearc of best focus, a number of such ports are fed simultaneously withradio frequency energy, a corresponding number of beams, each with adifferent scan angle, will be formed. It is obvious that such an antennamay be used to receive radio frequency energy as illustrated.

The just-mentioned design approach is adequate when the scan angle ofany beam of electromagnetic energy is less than, say 35. For greaterscan angles, the path length errors caused by unavoidable differences inthe lengths of the various electrical paths within the parallel-pathlens render the conventional Rotman/- Turner approach infeasible. Wehave found, however, that a decrease in the spacing between the antennaelements 45b through 45k from the spacing required by straightforwardapplication of the Rotman/Turner formulas is an effective way toincrease the scan angle of the radiated beam. Thus, after calculatingthe dimensions of a desired array antenna assembly, the spacing betweenadjacent elements may be decreased so that the following equation istrue:

S /S sin b/sin a where S is the spacing, in wavelengths,

of the antenna elements as calculated according to the Rotman/Turnerapproach;

a is the angular deviation of any feed port from the axis of symmetry ofan array antenna;

1; is the desired scan angle of the beam from the array antenna; and

S is the spacing, in wavelengths, between antenna elements required toobtain the desired scan angle b.

Thus, by decreasing the spacing between antenna elements, the scan anglemay be increased to a maximum of for a linear array of antenna elementswithout increasing the effect of path length errors in the array antennaassembly. It will be noted, in passing, that the decrease in spacing,additionally, increases the frequency of operation at which gratinglobes are formed by the illustrated array antenna assembly. Referring toFIG. 2 to illustrate the foregoing, let it be assumed that, inaccordance with the Rotman/Turner approach, the spacing, SRT, for a scanangle of 30 would be equal to the spacing between every other antennaelement. Then, in accordance with our concept, it may be easilycalculated that sin b equals 1 in the illustrated case. In other words,the scan angle, b, of the beam in the illustrated array corresponding tothe beam having a scan angle of 30 in a Rotman/Turner array would be 90.Obviously, the ratio between SRT and S could be selected as desired toincrease scan angle by any desired amount.

The physical size of known array antenna assemblies made with aparallel-plate lens and coaxial transmission lines is relatively great.That is, because the velocity of propagation of electromagnetic energyin either coaxial transmission lines or a parallel-plate lens with airas a dielectric approaches the velocity of propagation ofelectromangetic energy in free space, the use of elements (especiallywhen it is desired to focus and/or collimate radio frequency energypassing from or to an antenna with a large aperture) results in a lenssystem having a relatively long focal length. It follows, then, that thearc of best focus must be physically spaced a correspondingly largedistance from the antenna aperture. In applications in which physicalsize is at a pre-' mium, such a requirement of known parallel-platelenses militates against their use in array antennas. We have, however,by incorporating dielectric material having a dielectric constantgreater than the dielectric constant of air in a multi-beam arrayantenna assembly, effected a reduction in the velocity of propagation ofradio frequency energy therein, with a concomitant reduction in thephysical size of such an assembly. Thus, we have found that if an arrayantenna assembly is designed following the teachings of Rotman andTurner, the physical dimensions of the parallel-plate lens and thelength of the required transmission lines may be scaled down from thedimensions required with air as the dielectric material by a factorequal to the square root of the dielectric constant of the dielectricmaterial used as a substrate.

In a practical array antenna assembly using a parallelplate lens andtransmission lines it is not possible to overlook the effects of mutualcoupling and mismatches. That is, the VSWR for electromagnetic energywithin such an assembly must be carefully controlled in order to avoidexcessive insertion losses and internal reflections. Thus, in knownarray antenna assemblies it is common practice to provide matchedcoupling between the parallel-plate lens and the transmission lines, asby conventional impedance transformers. Unfortunately, as the frequencyof the radio frequency energy changes from a nominal design frequency,the use of matching sections such as impedance transformers (which arefrequency-sensitive) changes an inherently broadband antenna arrangementto a relatively narrow band one.

Even if the parallel-plate lens and transmission lines of known arrayantennas are perfectly matched at a design frequency, the problem ofcoupling discrete and separate elements with respect to each other topermit efficient power transfer remains. Thus, in order that radiofrequency energy be transferred efficiently between a parallel-platelens and a number of transmission lines by means of orthogonal couplingdevices, the positioning of such devices is critical, being optimum onlyat the design frequency. Consequently, when the frequency of the radiofrequency energy is changed from a design frequency, the efficiency ofpower transfer decreases. Again, an inherently broadband arrangement isconverted into a relatively narrow band arrangement.

The foregoing difficulties are obviated to a large degree by followingour concept of replacing the discrete and separate elements ofa radiofrequency lens sytem, i.e. the coaxial transmission lines andparallel-plate lens heretofore used in array antenna assemblies, withstripline or microstrip circuits integrally formed on a dielectricsubstrate along with the desired antenna elements. As a consequence, theparallel-plate lens, the transmission lines and the antenna elements maybe printed, as illustrated in FIG. 2, on one side of a dielectricsubstrate in such a manner as to permit matching sections to be formedintegrally therewith. Consequently, no frequency-sensitive circuitelements, as orthogonal probes, are inserted in the path of radiofrequency energy within the multi-beam array antenna assembly 10 (FIG.1). Further, because of the ease with which the shape of the printedmatching sections may be changed, it is possible to adjust the shape ofeach section for optimum performance. Therefore, by following ourconcepts in the design 'of a multi-beam array antenna for any particularapplication, the bandwidth of the resulting assembly will be limitedonly by the disposition of the antenna elements with respect to eachother.

It will be recognized that the dielectric constant of known soliddielectric materials varies with changes in temperature. Such acharacteristic change obviously changes the electrical length of thevarious constrained paths for radio frequency energy within thedescribed array antenna assembly. In the ordinary case the electricallength of each one of the various constrained paths variesproportionally with the original length thereof. It follows, then, thatthe electrical lengths of the various paths vary relatively with respectto each other with changes in temperature. Such relative changes, inturn, disturb the phase relationships between the various portions ofthe radio frequency energy in passing through the assembly so as tocause, for any beam other than the broadside beam, a shift in beamdirection. The amount of such shift increases with scan angle. It isevident, however, that conventional temperature control techniques,placing the array antenna assembly in a thermostatically controlledheating unit, may be used whenever necessary or desirable to avoid anydeleterious effects of changes in ambient temperature.

It will also be evident that many other changes and modifications may bemade in our preferred embodiment without departing from our inventiveconcepts. For example, the spacing between the antenna elements and thedisposition thereof may be varied as desired to change the shape ordirection of beams. Similarly, the number and disposition of the feedports may be varied to change the direction and number of beams.Additionally, the transmission lines between the antenna elements andthe parallel-plate lens may be broken to allow insertion of radiofrequency amplifiers in each one of such lines. Further, the surface ofthe dielectric substrate, and, if used, the surface of the dielectricsheet nearer to the printed circuits need not be planar. That is, suchsurfaces may be indented between the printed circuits in any convenientway to improve isolation between the different portions of such circuits. Finally, linear multi-beam array antennas of the type disclosedmay be arranged to form a planar array or may be used instead of asingle beam array which is scanned either electrically or mechanically.It is felt, therefore, that this invention should not be restricted toits disclosed embodiment but rather should be limited only by the spiritand scope of the appended claims.

What is claimed is:

1. In an antenna array assembly wherein any one, or ones, of a firstplurality of feedports disposed along an arcuate path may be actuatedwith microwave energy to energize a second plurality of antenna elementsdisposed to form a linear array, the direction of the beam, or beams, ofmicrowave energy propagated by such array being dependent upon the one,or ones, of the actuated feedports, an improved microwave lens andtransmission line arrangement interconnecting the first plurality offeedports with the second plurality of antenna elements, sucharrangement comprising a section of stripline including:

a. a printed circuit conductor having an irregular geometrical shape todefine a different constrained electrical path between each one of thefirst plurality of feedports and each one of the second plurality ofantenna elements; and,

b. a dielectric spacer overlying the center conductor, the dielectricconstant of such spacer being greater than unity.

2. The improved microwave lens and transmission line arrangement as inclaim 1 wherein the center conductor of the stripline includes:

a. a printed portion having a first and a second curved side, the feedports being coupled to points along the first curved side; and

b. a first plurality of printed lines, one end of each different onethereof being coupled to a different one of the first plurality ofantenna elements and the second end of each different one of such linesbeing coupled to points along the second curved side of the printedportion.

3. The improved microwave lens as in claim 1 wherein the electricallength of each different constrained electrical path between any one ofthe feedports and successive ones of the antenna elements differsprogressively by an amount equal to the difference in the electricallength between any successive pair of antenna elements and a planarwavefront of microwave energy.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Inventor(s) DonaldH. Archer, Robert J. Prickett and Curtis Hartwig It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

In the Specification Column 1, line 28, "paral1el plane should be-parallelplate-- Column 3, line 23, "sisgnals" should be -signals Column3, line 40, "170" should be -.l7o-

Column 4, line 4, after 'dielectri'c" add -sheet-- Column 5, line 27,change to --degrees-- Column 5, line 43, change "of" to --on- In theClaims Column 9, line 11 after "circuit" add -center-- Signed and Scaledthis twenty-eight D ay Of October 1975 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner ofParentsand Trademarks UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTIONpatent 3 ,761,936 Dated eptember 25 1973 Inventor(s) Donald H. Archer,Robert J. Prickett and Curtis Hartwig It is certified that error appearsin the above-identified patent and that said Letters Patent are herebycorrected as shown below:

In the Specification Column 1, line 28, "parallel\plane should be-parallelplate-- Column 3, line 23, "sisgnals" should be -signals-Column 3, line 40, "170" should be l'7o- Column 4, line 4, after"dielectric" add sheet-- Column 5, line 27, change to -degrees-- Column5, line 43, change "of" to -on In the Claims Column 9, line 11 after"circuit" add center-- Signed and Sealed this twenty-eight D ay OfOctober 1 975 [SEAL] Attest:

RUTH C. MASON C. MARSHALL DANN Arresting Office'r Commissioneruj'Parents and Trademarks

1. In an antenna array assembly wherein any one, or ones, of a firstplurality of feedports disposed along an arcuate path may be actuatedwith microwave energy to energize a second plurality of antenna elementsdisposed to form a linear array, the direction of the beam, or beams, ofmicrowave energy propagated by such array being dependent upon the one,or ones, of the actuated feedports, an improved microwave lens andtransmission line arrangement interconnecting the first plurality offeedports with the second plurality of antenna elements, sucharrangement comprising a section of stripline including: a. a printedcircuit conductor having an irregular geometrical shape to define adifferent constrained electrical path between each one of the firstplurality of feedports and each one of the second plurality of antennaelements; and, b. a dielectric spacer overlying the center conductor,the dielectric constant of such spacer being greater than unity.
 2. Theimproved microwave lens and transmission line arrangement as in claim 1wherein the center conductor of the stripline includes: a. a printedportion having a first and a second curved side, the feed ports beingcoupled to points along the first curved side; and b. a first pluralityof printed lines, one end of each different one thereof being coupled toa different one of the first plurality of antenna elements and thesecond end of each different one of such lines being coupled to pointsalong the second curved side of the printed portion.
 3. The improvedmicrowave lens as in claim 1 wherein the electrical length of eachdifferent constrained electrical path between any one of the feedportsand successive ones of the antenna elements differs progressively by anamount equal to the difference in the electrical length between anysuccessive pair of antenna elements and a planar wavefront of microwaveenergy.